API/CLI context enhancements (#11331)

* API: expose context size of loaded models

* CLI: add context UX

This adds a column in the ps output to show the models context size.

server/routes.go

@@ -1404,6 +1404,9 @@ func (s *Server) PsHandler(c *gin.Context) {
 			Details:   modelDetails,
 			ExpiresAt: v.expiresAt,
 		}
+		if v.Options != nil {
+			mr.ContextLength = v.Options.NumCtx / v.numParallel
+		}
 		// The scheduler waits to set expiresAt, so if a model is loading it's
 		// possible that it will be set to the unix epoch. For those cases, just
 		// calculate the time w/ the sessionDuration instead.